The present invention relates to glass for encapsulating a semiconductor. More particularly, the present invention relates to glass for hermetically encapsulating an element such as silicon diode, a light-emitting diode, a thermistor, and an electrode material such as Dumet wire for electrically connecting these elements, and relates to a glass encapsulator for encapsulating a semiconductor prepared therefrom.
A small-sized electronic semiconductor part, such as silicon diode, a light-emitting diode, and a thermistor, is normally in DHD (Double Heat Sink Diode) form. In more detail, such a semiconductor element is clamped between electrode materials such as Dumet wire, and then is surrounded by a glass tube. The entire assembly is then heated to a predetermined temperature so that the glass tube softens and deforms to effect an hermetic seal. In general, this heating temperature is the value at which the viscosity of glass reaches 106 dPaxc2x7s and is referred to as xe2x80x9csealing temperaturexe2x80x9d. The sealing temperature of glass is required to be not higher than the maximum allowable temperature of the semiconductor to be encapsulated so that the electrical properties of the semiconductor are not impaired by the heating temperature. The maximum allowable temperature of semiconductors varies with type and design. Since semiconductors exhibit a maximum allowable temperature of about 710xc2x0 C. at the most, it is important that the sealing temperature of the glass is not higher than 710xc2x0 C. Another requirement for the glass relates to its thermal expansion coefficient. This requirement is that the thermal expansion coefficient of the glass should conform to that of Dumet wire, which most commonly is used as an electrode material. In more detail, the thermal expansion coefficient of the glass needs to be from 85xc3x9710xe2x88x927 to 105xc3x9710xe2x88x927/xc2x0 C. at a temperature of from 30xc2x0 C. to 380xc2x0 C.
Glass that has heretofore been used for encapsulating a semiconductor and that meets above-described requirements was lead silicate glass containing PbO in an amount as great as 45 to 75% by weight. This is because PbO has an extremely great effect of lowering the viscosity of glass while forming stable silicate glass. For example, glass, for encapsulating a semiconductor, containing PbO in an amount of 46% by weight exhibits a sealing temperature of about 700xc2x0 C. Glass, for encapsulating a semiconductor, containing PbO in an amount of 60% by weight exhibits a sealing temperature of about 655xc2x0 C.
In recent years, environmental pollution by harmful ingredients, such as lead, cadmium, and arsenic, has been an issue. It has been required that industrial products be free of these harmful ingredients. In the industry of electronic parts, too, it has been positively endeavored to practice the use of lead-free solder. Further, it has been desired that glass for encapsulating a semiconductor be free of PbO.
An attempt to remove lead from lead glass, which can be used as a constituent of electrical apparatus and electronic parts to seal stably with Dumet, is disclosed in JP-A-6-206737 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d). However, the target of this attempt is to render lead glass having a PbO content of from about 20 to 30% by weight. The glass having a PbO content of from about 20% to 30% by weight is glass for sealing a bulb in fluorescent lighting or in an incandescent lamp. This glass material originally has a sealing temperature of about 750xc2x0 C. In addition, the lead-free glass disclosed in the above cited JP-A-6-206737 exhibits a sealing temperature as high as about 790xc2x0 C. Therefore, the glass material of the type disclosed above can by no means attain a sealing temperature of not higher than 710xc2x0 C. as required for glass that encapsulates a semiconductor.
An object of the present invention is to provide glass, for encapsulating a semiconductor, which is substantially free of lead or other harmful ingredients, but which exhibits a sealing temperature of not higher than 710xc2x0 C. and can be sealed stably with Dumet. Another object of the present invention is to provide is sealing glass encapsulator prepared from the above-described glass.
These and other objects of the present invention have been accomplished by glass, for encapsulating a semiconductor, comprising:
at least two of Li2O, Na2O and K2O; and
B2O3,
wherein said glass is free of lead, and
wherein, when said glass has a viscosity of 106 dPaxc2x7s, the temperature of said glass is not higher than 710xc2x0 C.
Furthermore, these and other objects of the present invention have been accomplished by glass, for encapsulating and semiconductor, comprising:
SiO2 in an amount of from 40 to 70% by weight;
B2O3 in an amount of from 5 to 20% by weight;
Al2O3 in an amount of from 0 to 15% by weight;
MgO, CaO, SrO, BaO and ZnO in a total amount of from 0 to 45% by weight; and
at least two of Li2O, Na2O and K2O in a total amount of from 5 to 25% by weight,
each based on the total amount of said glass.
Moreover, these and other objects of the present invention have been accomplished by a glass encapsulator, for encapsulating a semiconductor, comprising glass including:
at least two of Li2O, Na2O and K2O; and
B2O3,
wherein said glass is free of lead, and
wherein, when said glass has a viscosity of 106 dPaxc2x7s, the temperature of said glass is not higher than 710xc2x0 C.
Also, these and other objects of the present invention have been accomplished by a glass encapsulator, for encapsulating a semiconductor, comprising glass including:
SiO2 in an amount of from 40 to 70% by weight;
B2O3 in an amount of from 5 to 20% by weight;
Al2O3 in an amount of from 0 to 15% by weight;
MgO, CaO, SrO, BaO and ZnO in a total amount of from 0 to 45% by weight; and
at least two of Li2O, Na2O and K2O in a total amount of from 5 to 25% by weight,
each based on the total amount of said glass.
Furthermore, these and other objects of the present invention have been accomplished by a method for encapsulating a semiconductor element, comprising encapsulating the semiconductor element with an encapsulator, using a glass tube made of above-mentioned glass.